There is no 3-dimensional model for studying neural tissues, outside of explanting whole tissues from animals. For example, in the retina, degenerations of retinal ganglion cells (RGCs) in diseases like glaucoma or of photoreceptors and retinal pigment epithelium in diseases like age-related macular degeneration have generated considerable interest understanding the integration of stem cells or stem cell-derived neurons into neural tissues. But study of cell replacement therapies for such diseases outside of the whole animal has focused on a limited group of experimental approaches, either examining the explanted whole retina in culture, or studying the individual cell types in 2-dimensional cultures. Missing is any opportunity to learn about cellular development or integration in the 3-dimensional (3D) environment these cells normally experience. In addition, there are no 3-dimensional organ replacement therapeutic approaches for neural tissue. Here we will reverse this paradigm and create a new model system that combines in vitro advantages of experimental control and screening capability with in vivo advantages of studying neurons in their 3D environment, building towards organ replacement therapies for the nervous system. We will re-create the retina from its basic cell types in culture using 3D biodegradable scaffolds to provide a critical new model system to study how the retina develops, functions, and operates in response to disease or injury, and to study how stem cell-derived neurons synaptically integrate with their neighbors. Specifically, we will create 3D tissue models of the neural retina with retinal ganglion cells and amacrine cells, characterize and optimize their synaptic connectivity, and examine the ability of retinal progenitor cells added to these 3D tissue models to proliferate, differentiate, and integrate synaptically. Our goal is to develop 3D neural tissues for studying neural development, and ultimately for tissue replacement therapies. PUBLIC HEALTH RELEVANCE: Here we will create for the first time a three-dimensional neural tissue, the retina, ex vivo. This will allow for a new way to study stem cell integration into neural tissues and, as importantly, will build towards tissue replacement therapies for the nervous system.